CODEWITHSUNDEEP
pythonpython-unittest
Henrique Andrade
Henrique Andrade

Reputation: 991

Python mock a method from a class that was not imported

Take this example, func_to_test_script.py

from module import ClassA

def func_to_test():
    instance_b = ClassA.method_a()
    foo = instance_b.method_b()

method_a returns an instance of class ClassB.

I want to mock the calls of methods method_a and method_b, so I do

@mock.patch("func_to_test_script.ClassA", ClassAMock)
@mock.patch("func_to_test_script.ClassB", ClassBMock)
def test_func_to_test(self):
    # test

I can do this with ClassA (that was imported in func_to_test's file), but with ClassB I get the error

AttributeError: <module 'module' from 'func_to_test_script.py'> does not have the attribute 'ClassB'

Upvotes: 0

Views: 1065

Answers (1)

Niel Godfrey P. Ponciano
Niel Godfrey P. Ponciano

Reputation: 10709

First, it will really fail because ClassB is not defined nor imported in func_to_test_script.py. But even if it is, there is still no need to patch it because it wouldn't take effect anyways. Why? Because the instance of ClassB will come from the response of ClassA, which you already mocked.

What you can do is control it from the mock of ClassA:

@mock.patch("func_to_test_script.ClassA")
def test_func_to_test(self, mock_class_a):
    mock_class_a.method_a.return_value.method_b.return_value = "value of foo"
    ...

Upvotes: 2

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